Wood preserving compositions are well known for preserving wood and other cellulose-based materials such as paper, particleboard, textiles, rope, etc., against organisms, including fungi and insects, responsible for the destruction of wood. Many conventional wood preserving compositions contain copper amine complexes. Copper amine complexes have been used in the past because the amine solubilizes the copper in aqueous solutions. The copper in such copper amine complexes is obtained from a variety of copper bearing materials, such as copper scrap, cuprous oxide, copper carbonate, copper hydroxide, a variety of cuprous and cupric salts, and copper bearing ores. The amine in such copper amine complexes is normally obtained from an aqueous solution of ammonia and ammonium salts, such as ammonium carbonate, and ammonium sulfate, ethanolamines, et cetera. For example, U.S. Pat. No. 4,622,248 describes forming copper amine complexes by dissolving copper (II) oxide [CuO] (also known as cupric oxide) in ammonia in the presence of ammonium bicarbonate.
However, copper ammonia preservatives can affect the appearance of the treated wood giving surface residues and undesirable color. In recent years, many amine-containing compounds, such as the ethanolamines and aliphatic polyamines, have been used to replace ammonia to formulate water-soluble copper solutions. These compounds were chosen because of their strong complexing ability with copper and because they are essentially odorless. U.S. Pat. No. 4,622,248 discloses a method of preparing copper amine complexes by dissolving a mixture of copper (II) carbonate [CuCO3] and copper (II) hydroxide [Cu(OH)2] in ethanolamine and water. The complexing amine (i.e., the ligand) and copper (II) ion combine stoichiometrically and thus the weight ratio of reagents will be different for each complexing amine. However, copper amine based preservatives have higher copper loss due to leaching as compared to traditional copper based preservatives such as chromated copper arsenate (CCA).
Other metal compounds have also been used as biocides in wood and other cellulosic materials. Generally, the metal compounds are used in solution as metal complexes or metal ions. For example, zinc compounds, dissolved in a base, such as ammonia or an acid such as acetic acid solutions have been used in biocidal applications for wood. However, the biocidal efficacy of dissolved zinc compounds has been found to be significantly less than that of copper. Therefore, certain fungi, such as copper-tolerant brown rots, remain difficult to control. Additionally, zinc compounds dissolved in ammonia have a strong odor and pose other environmental/health concerns, and zinc compounds dissolved in acids have a tendency to leach into the environment when used in service. Thus, there continues to be a need for improving the biocidal efficacy of water-based, metal-containing wood preservatives.